OBSERVATIONS ON IN-SITU DEGRADATION OF FORAGE CELL COMPONENTS IN ALFALFA AND ITALIAN RYEGRASS

The rate and extent of degradation of forage feed fractions contained in alfalfa and Italian ryegrass hays were determined. Nylon bags fille d with 4 g of each forage were suspended in the rumen of two cannulate d cows immediately before feeding and incubated for 10 different times (0, 2, 4, 8, 12, 24, 48, 72, 120, and 168 h). The alfalfa hay, which had lower NDF, showed a lower extent, but a higher rate, of NDF degrad ation than the Italian ryegrass (41.1 vs. 59.8% and 4.64 vs. 2.91%/h, respectively). Alfalfa cell walls were degraded more rapidly than Ital ian ryegrass even though their lignin content was higher. The hemicell ulose fermentation of alfalfa showed a longer lag time (13 h) and an u ndegradable fraction nearly twice that for Italian ryegrass (63.3 vs. 37.1%). Cellulose from alfalfa was degraded at a higher rate than NDF or ADF, indicating that cellulose may be the primary site of hydrolysi s of the cell wall in the rumen. Calculations based on in situ degrada bility indicate that alfalfa can have a higher inclusion than Italian ryegrass in diets for dairy cows because of lower NDF and greater avai lability of cell contents.